Artificial hands having a single degree of freedom in which fingers and a thumb may be caused to approach and withdraw from each other by an electrical actuator are known and are supplied, for example, by Viennatone. Control circuits for such hands are described in Patent Specifications Nos. GB-A-1142417 and 1360933 and derive control signals derived from myoelectric currents that occur on contraction of a muscle or group of muscles to derive command signals for two control channels, one of which serves to open the hand and the other to close the hand. Although the fingers and thumb can be positioned with such mechanisms and wearers can pick up objects, these known mechanisms do not have any built-in response mechanism to alter their function when they contact an object to be picked up, nor do they allow the gripping force that they exert to be adjusted automatically to hold a fragile object without crushing it and to exert only that force that will prevent the object from slipping through the hand.